This invention relates in general to the manufacture of vehicle wheels and in particular to a tool and method for forming lug holes through a vehicle wheel hub.
Vehicle wheels include an annular wheel rim that supports a pneumatic tire. A wheel disc typically extends across the outboard end of the wheel rim and is formed having a pleasing esthetic shape. The wheel disc usually includes a central wheel hub supported within the wheel rim by a plurality of radial spokes. Apertures formed through the wheel hub allow attachment to a vehicle axle.
Light weight vehicle wheels cast from alloys of aluminum, magnesium, and titanium have become increasingly popular. Such wheels may be cast as one piece and then finished with a number of machining operations or assembled from several components that also are machined to final dimensions. Regardless of the method used, the manufacture of vehicle wheels is highly automated.
One of the steps that are required to manufacture a vehicle wheel is the forming of a plurality of lug holes through the hub of the vehicle wheel. When a vehicle wheel is mounted upon an axle, a plurality of lug bolts extending from an axle hub are received by corresponding lug holes in the wheel hub. A chamfer formed at the inboard end each lug hole guides the end of each of the lug bolts into the respective lug hole. Each of the lug bolts cooperate with a corresponding lug nut, that is seated upon a conical seat formed at the outboard end of each lug hole, to secure the vehicle wheel to the wheel hub.
Referring now to the drawings, a typical lug hole 10 is illustrated in FIG. 1 that extends through a hub portion 12 of a vehicle wheel, as shown in section. The lug hole 10 extends from an outboard surface 16 through the wheel hub 12 and to an inboard surface 18. As also shown in FIG. 1, the lug hole 10 includes an outboard end counterbore 22 that receives the lug nut (not shown). A conical seat 26 is formed in the base of the counterbore 22. The lug hole 10 further includes a circular recess 20 formed at the inboard end of the lug hole 10 that receives a nut, such as a Tinnerman® nut (not shown). A chamfer portion 24 is formed in the base of the circular recess 20 of the lug hole 10. A lug hole land 28 extends between the chamfer portion 24 and the conical seat 26. A lug bolt 29 disposed in the lug hole 10 is outlined with dashed lines.
The lug hole 10 is formed with a highly automated process that is illustrated by the flow chart shown in FIG. 2. The various tools used to form the lug hole 10 are mounted upon a multiple tool drilling head in a wheel drilling machine. The process begins in functional block 30 with the wheel being clamped upon a wheel drilling machine jig with the outboard end facing the multiple tool drilling head. Typically, when the wheel is formed, the circular recess 20 is cast integrally to the wheel. Alternatively, the circular recess 20 may be machined before the wheel is clamped upon the wheel drilling machine jig for forming the lug hole 10. In functional block 31, a pilot hole for a lug hole is drilled through the wheel hub with a spiral twist drill. Drilling the pilot hole also forms the lug hole land 28. The wheel is then indexed and additional lug hole lands are drilled. In a similar manner, the wheel is indexed after each of the following operations to permit repeating the specific operation for each lug hole. Next, the outboard end of the lug hole 10 is counterbored with a counterbore tool in functional block 32. A countersink is used in functional block 34 to form the conical seat 26 in the base of the counterbore 22. Then a reamer is used in functional block 35 to polish the wall of the counterbore 22. The wheel is then rotated 180 degrees upon the wheel jig in functional block 36 to expose the inboard surface of the disc to the multiple tool drilling head. Finally, in functional block 38 the chamfer portion 24 is formed in the base of the circular recess 20 by using a chamfer tool.
As described above, the process for forming a lug hole requires numerous machining operations and a number of different tools. Because a vehicle wheel typically includes five lug holes, it is apparent that a great deal of time and effort is required to form the lug holes. Accordingly, it would be desirable to reduce the number of machining operations and the number of tools to reduce both the time required to finish a wheel and the number of different tools that must be carried in inventory at the manufacturing facility.